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W. M. Townsend 《Equine Veterinary Education》2016,28(12):705-711
Cataracts can be developmental or acquired lesions and cause minimal or significant visual impairment. The ability to identify cataracts and determine the likely effect on the visual potential of the horse is an important part of an equine ocular examination. Cataract surgery is the only treatment for those cataracts that cause significant visual impairment. Understanding appropriate patient selection and potential post operative complications is important so that owners can be appropriately advised of their options. 相似文献
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The present studies are based on the feedback provided by fish farmers practicing composite fish culture of carps. According to them, fish habitats are affected by pesticides draining from agricultural fields into their catchments, especially during the rainy season. The lenses of most of the cultured fish became opaque, resulting in poor overall growth. In the literature, there was mounting evidence of pesticide toxicity involving multiple tissues. However, the fish visual system has never been investigated particularly from the toxicological perspective. In this regard, we carried out comparative toxicological studies on the lens of Cyprinus carpio communis using three different sublethal concentrations (0.038, 0.062 and 0.126 p.p.m.) of monocrotophos along with untreated controls for 30 days. Lenses from all the groups were extracted and preserved in gluteraldehyde and osmium tetraoxide and dehydrated in increasing grades of acetone. After dehydration, tissues were conducted with gold to observe under SEM. The fish exposed to monocrotophos developed cataract. Furthermore, when fish from the monocrotophos-treated tanks were transferred to normal environmental conditions for the next 60 days, progressive lens degeneration was noted. To conclude, monocrotophos induces irreversible cataractous changes in the lens of C. carpio communis . The fish visual system has many similarities to mammals and may serve as a good model for comparative toxicologic and ophthalmologic studies. 相似文献
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根据电磁场理论推导出了左手材料的传输函数,并数值计算了介电常数和磁导率偏移理想值时,传输函数所发生的变化.数值计算表明:传输函数对介电常数和磁导率的偏移非常敏感,完美的左手材料透镜对偏移量的要求十分苛刻.因此,要得到工程意义上完美的左手材料透镜是相当困难的. 相似文献
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为了建立精确测定X光透镜发散度的实验方法,提出了有效X光源的概念,这样可以得到X光束发散度的准确值.推导出了X光束发散度的理论计算公式.零点扫描实验方法证明了理论公式的正确性.晶体转动实验方法测量了X光束的发散度,与理论值符合得很好,晶体转动实验方法建立.晶体转动实验方法应用到对X光透镜发散度的测定可以消除分析晶体不完整性的影响,精确性很高. 相似文献
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[目的]为提高解剖镜的放大倍数和打破显微操作的极限开辟新途径。[方法]利用自制球形液滴的放大作用,对附地菜受精前、后的子房进行了观察和解剖,并用手工方法分离出了附地菜的胚珠和球形幼胚。[结果]在解剖镜下测得液滴内放大的附地菜子房的直径约为1.1mm;用吸水纸将液滴除去后,测得附地菜子房的实际直径约为0.7mm;球形液滴将附地菜子房放大了约1.57倍。球形液滴对光线有一定的聚集作用。在具有放大作用的球形液滴中,分离出受精后在胚珠中发育的球形幼胚(直径约0.1mm),浅柒制片后,在显微镜下观察到幼胚的外形为球形。[结论]球形透明液滴可以提高解剖镜对液滴内物体或结构的放大倍数。 相似文献
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